1. Field of the Invention
This invention relates to laparoscopic tools for performing surgical procedures and, more particularly, to a tool useful for tightening a ligature through a laparoscopic cannula.
2. Reference to Copending Application
Reference is made to copending patent application Ser. No. 08/068,411 filed May 27, 1993 entitled "Universal Gastric Band" now U.S. Pat. No. 5,601,604 by one of the present inventors.
3. Prior Art
There are many occasions when it is necessary to place a strap, belt, or ligature around a tissue or a prosthesis to fix it in place. Such a ligature can take the form of a cable tie commonly used for bundling electrical wires or a band such as a gastric band for encircling a stomach. Recently, laparoscopic methods and tools have been developed which enable the placement of such ligatures around organs or tissues without the need for open surgery. Unfortunately, it is difficult to manipulate the ends of such ligatures through a laparoscopic cannula inasmuch as the cannulae are rarely more than 12 millimeters in diameter. Moreover, a 3-dimensional operation such as fastening a ligature around a tissue must be accomplished by viewing the actual procedure on a 2-dimensional screen. Thus, it is inherent in laparoscopic surgery that spacial relationships must be arduously learned through practice.
Special bands have been devised to encircle tissue such as the stomach. Such a band is described, for example, in co-pending U.S. patent application Ser. No. 08/068,411 to one of the present inventors (V. L. Vincent). This band, which is designed to encircle a portion of the stomach to control overeating, has been fitted with a buckling mechanism whereby the band can be locked in an encircling position around the stomach. A balloon portion of the band is then inflated to further compress the walls of the stomach as required to produce a stoma of the correct dimension. The gastric band or ligature is comprised of a tunnel/buckle end and a free end with a strap or body portion therebetween. The free end of the strap is passed through the buckle and pulled snug until a "head" component near the free end exits the buckle, effectively locking the ligature in an encircling position. This maneuver can be done with existing laparoscopic surgical instruments, using one instrument to hold a tab on the buckle and another to pull the strap through the buckle. However, this leaves open a wide range of possibilities as to what instruments are used; blunt forceps, sharp tipped dissecting forceps, gaspers or even closed scissors. Whatever the choice of prior art instruments, the possibility of damage to the closure components or the tissue exists.
Bands such as that described above are difficult to fasten in position around the stomach through a laparoscopic cannula for the stated reasons. After the free end of the band is passed through the conduit in the buckle portion, the free end must be pulled tight with respect to the buckle portion so that a locking means can engage the buckle. Such maneuvering of the free end through the buckle and pulling and tensioning the strap to pull the locking means through the buckle may result in damage to the strap or to the buckle, or to surrounding tissue. This is particularly true if one or both of the instruments used to tighten the band slip loose abruptly and puncture or otherwise injure surrounding tissue. It is therefore desirable to provide an instrument for tightening a strap laparoscopically and which will provide a smooth, in-line traction on the free end and eliminate the problems presented by prior art tools.